Activities like sprinting require levels of energy that are greater than the body can produce with the aerobic (with oxygen) metabolism. For these activities, the body relies on anaerobic (without oxygen) processes.The body still takes in oxygen during these activities but creates the energy for the activity using a process that doesn’t require oxygen.
Lactic acid is a byproduct of anaerobic metabolism. It builds up to high levels within the muscles and eventually leads to
fatigue during these high intensity activities.